1. Field of Invention
The present invention relates to a method for preparing an anti-bacterial fiber. More particularly, the present invention relates to a method for preparing a γ-polyglutamic acid (γ-PGA) fiber having high water-absorption and antibacterial properties.
2. Description of Related Art
High water-absorption materials have water absorptivity, and can retain water of tens or hundreds folds of their own weight after absorption, thus having a quite wide application range. Conventionally used high water-absorption materials are mainly divided into two types. One is carbohydrate based, such as polysaccharides. The polysaccharides can be starch, chitosan, sodium alginate, and carboxymethyl cellulose (CMC), for example. These materials are natural materials, and have good biodegradability, but are limited in application due to limited water absorptivity (generally not higher than 10 folds). The other type is chemically synthesized polymers, such as polyacrylate or poly(vinyl alcohol). These materials have better water absorptivity than the above natural materials do. They also have some problems such as complicated preparation and potential release of toxic monomer and base residues. Furthermore, these chemically synthesized polymers are not biodegradable, and thus will cause hazard to environment after disposal. Therefore, in view of the environment protection requirement, the natural polysaccharide materials having poor water absorptivity are still generally selected to be used as the main water-absorption material.
Conventional high water-absorption materials are commonly prepared in a form of hydrogel or film. For example, Japanese Patent Publication No. 94-322358 discloses a method for cross-linking of a γ-PGA solution by a γ-ray cross-linking technology, to prepare a high water-absorption hydrogel. Furthermore, it is also mentioned in U.S. Pat. No. 4,572,906 that a water-absorption film dressing can be prepared with a mixture of chitosan and gelatin. However, the film and hydrogel disclosed in these technologies cannot provide a flow guiding function when they contact with a liquid. Because only the flat surfaces of the film and hydrogel can contact with the liquid, the overall water absorption rate is low. Thus, it results in limited application.
However, if a water-absorption material is fiberized, the contact area may be efficiently increased, thereby increasing the water absorption rate. Moreover, the structure of the fiber may further provide the flow guiding function, so as to increase the water absorption rate. U.S. application Ser. No. 12/757,288 discloses that natural γ-PGA can be spun out in a partially cross-linked form, to prepare γ-PGA fibers having high water absorptivity. By this technology, the problem of the low water absorption rate of the conventional natural water-absorption materials is fully solved.
The γ-PGA fibers above have good biodegradability. Thus, if a part of the material is decomposed while using, the whole structure of the fibers will be destroyed and disintegrated, so that the water absorptivity thereof is lowered. On the other hand, when a part of the material is decomposed, oilgopeptides or amino acid monomers may be formed. However, because these substances are nutrient sources of microorganisms, growth of microorganisms are easily caused. If such a fiber directly contacts with a human body, or is prepared into a dressing material for health care, infection with the organisms may occur. In order to prevent the occurrence of such a hazard, a sufficient antibacterial ability is required to introduce into this fiber.
In the prior art, an antibacterial treatment method of fibers is generally attaching an organic or an inorganic antibacterial material to fibers. The inorganic antibacterial material is generally a support containing metal ions (e.g., Ag+, and Zn2+), or metal nanoparticles (for example, silver nanoparticles). The inorganic antibacterial material above can release the metal ions or the metal nanoparticles above to bind cellular proteins of microorganisms to inactivate the microorganisms, thereby to achieve the antibacterial efficacy. The antibacterial effect is generally relatively long acting. However, a process for attaching the inorganic antibacterial material on the fibers is complicated and highly cost (as known from U.S. Pat. Nos. 6,333,093, 6,451,003, and 6,267,782), and there are also problems such as cytotoxicity and low releasing rate, and thus the overall antibacterial effect is limited. Furthermore, as for the organic antibacterial materials, a quaternary ammonium salt is commonly used as disinfectant and antibacterial agent of the fiber in the prior art, and also has the advantage of long-acting antibacterial effect. However, the quaternary ammonium salt has a poor thermal stability and cannot be used in a process of plastic or fiber spinning, thus having limitations in application.
Therefore, it is necessary to develop a preparation method having simple process and low production cost, to obtain a fiber having antibacterial property and high water absorptivity.